Maximum allowable deflection rolls 1

[crigido3d]

Hi friends:
I am working in the design of a 3-Roll Plate Bending Machine of pyramidal disposition. I am writing to enquire about the deflection rolls. I would like to know what is the maximum value or limit permissible deflection for the rollers.
I suppose that exist standards or codes that specify these values (L/500, L/1000, etc.), but I could not find information about it. Exist some code ASME or any other reference about this? Or am I wrong?

greetings



"Persistence prevails, like a stream that is temporarily blocked by boulders and then collects force enough to overflow onward."

 

[MikeHalloran]

I'm not aware of a code that deals with such internal issues of machinery.

It should be possible to work backwards from the specifications of the target machine, e.g. plate width, thickness, material, and radius of curvature to be achieved, to balance the roll diameter and span, or figure out whether backing rolls are required.

It would be easier to look in your company standards, if you have any and they can be retrieved.

It would still be easier to reverse-engineer some of the units your company has made before, so as to infer what the standards might be, if they existed and were recoverable.

If your company hasn't made anything similar before, build and test one as fast as you can, so you can start writing your own internal standards.



Mike Halloran
Pembroke Pines, FL, USA

 

[MiketheEngineer]

Sounds like you might be building a "level-line". While I doubt any mfg would talk to you about your own design - you be able to glean some good info from a sales engineer??

Google "Level Line"

 

[crigido3d]

I plotted deflection Vs. roller diameter. My problem is find in this range which is the optimum value of design. Is true, I do not believe that exist nothing of this in the codes, though I did think that there would be something to the structural case (see image).
I have been trying to get in touch with sales engineer, but I had no luck.

Many thanks to both of your answers.

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"Persistence prevails, like a stream that is temporarily blocked by boulders and then collects force enough to overflow onward."

 

[MikeHalloran]

The optimum deflection is zero. You are not building a floor, you are building a machine tool.
The tool's purpose is to roll thick steel plate into cylinders, or occasionally segments of cylinders.
If the rolls deflect too much at their center, the plate will get less curvature in the center than at the ends of the rolls, so the cylinders will come out biconical, or some other nonideal shape.
If the rolls themselves are very large in diameter, they will be stiff in bending, but there will be a lower limit on the diameter of the workpiece you can roll.
You have to find a compromise somewhere in that multidimensional space.


Mike Halloran
Pembroke Pines, FL, USA

 

[Compositepro]

I think you would make the rollers as large in diameter as possible while still being able to roll the work to the smallest required diameter. If these rollers are then not stiff enough, you use strong backs, which is a stiff frame that supports the main rollers with small rollers at intermediate points along the length of the main roller.

 

[crigido3d]

"If the rolls themselves are very large in diameter, they will be stiff in bending, but there will be a lower limit on the diameter of the workpiece you can roll.
You have to find a compromise somewhere in that multidimensional space"

Excellent point! I´m work about this.

"I think you would make the rollers as large in diameter as possible while still being able to roll the work to the smallest required diameter. If these rollers are then not stiff enough, you use strong backs, which is a stiff frame that supports the main rollers with small rollers at intermediate points along the length of the main roller"


Thanks, I will also evaluate this.


Thank you for sharing their points of view. Has been a great help to me.


"Persistence prevails, like a stream that is temporarily blocked by boulders and then collects force enough to overflow onward."

 

[MikeHalloran]

Strongbacks and small idler/transfer rollers are one solution to the radius/deflection problem.

Another, used in rolling mills, is to back up the small radius roll with a much bigger radius roll, so the back side of the small roll is supported continuously.

Whether you need either depends on the range of workpieces for which you are designing, so far unrevealed.

Whether either scheme will work in a plate bending machine is another question you have to answer, because a full circle cylinder of bent plate is a common work product, so the depth available for structure behind the 'top' roll is not unlimited.

Life also gets interesting when you go to remove that bent cylinder from the bending machine; usually either the top cylinder or one entire end frame is demountable for that purpose.



Mike Halloran
Pembroke Pines, FL, USA

 

[MintJulep]

The optimum deflection is zero.

Well actually, the optimum is that the line of contact between the roll and the material being worked is a straight line.

So you could compensate for the inevitable deflection by making the roll a bit crowned in the unloaded state. Or so it seems to me, who has never worked with such beasts.

 

[Compositepro]

Crowned rollers is a possibility, although that's usually only an option where you can operate at a preknown and constant load.

Skewed rolls is also possible, where the roll axes are not parallel. But this is really only useful for nip rolls and probably not useful for bending rolls where three rollers are involved.

And large back-up rolls like in a Z-mill(

http://en.wikipedia.org/wiki/Z-mill)

probably wouldn't work either because the rollers would get in the way of the work piece.

 

[GregLocock]

I think you need to work back from the spec for the final product (bent plate) rather than relying on some rule of thumb derived for lazy engineers or overworked drafters to use.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[crigido3d]

Finally I resorted to the standard. There I was able see what are the finished product tolerances (bent plate). Then I adjusted my design for meet such specifications.
Thank you very much to all for your feedback.
Sorry for my english!
Greetings!

"Persistence prevails, like a stream that is temporarily blocked by boulders and then collects force enough to overflow onward."

 

[MikeHalloran]

Don't apologize for your English; it's good enough to get your point across.


Mike Halloran
Pembroke Pines, FL, USA